Prospects of Miscanthus x giganteus for PAH phytoremediation: A microcosm study

Phytoremediation of large surface areas using crop cultivation appears as an attractive strategy to allow for long-term but economically viable site rehabilitation programs. The contribution of Miscanthus x giganteus root exudates to the biostimulation of PAH degradation was recently demonstrated using in vitro assays. The aim of this work was to characterize the phytoremediation potential of this perennial grass in the situation of PAH polluted soils. For this purpose, three factors affecting bioremediation, namely the nature of soil organic contaminants (spiked phenanthrene and pyrene each at 100 mg/kg dry soil), bioaugmentation (with a PAH-degrading microflora) and planting (with Miscanthus x giganteus), were arranged according to a full factorial design in pot experiments. Effects of each factor (alone or in combination) were assessed on soil bacterial communities (total culturable bacteria and PAH-degrader enumerations, 16S rDNA molecular diversity analysis) and PAH dissipation. Results showed that contamination was the main factor positively influencing the development of degrader populations. Phenanthrene dissipation was observed regardless the presence of plants or initial PAH-degrading bacterial inoculum whereas significant decreases in pyrene contents were positively influenced by bioaugmentation and to a lesser extent by planting. The ability of plants to maintain a degrading rhizosphere microflora thus enhancing the dissipation of recalcitrant compounds in polluted soils would deserve further investigations.

► The development and the maintenance of a PAH-degrading microflora were observed in the rhizosphere of Miscanthus x giganteus.
► Bioaugmentation did not affect numbers of PAH degraders but allowed for enhanced PAH dissipation.
► Planting with Miscanthus x giganteus positively influenced dissipation of recalcitrant compounds such as pyrene.